1. Field of the Invention
The present invention relates to a method of automatically discriminating and separating scraps containing copper, which is an impurity element, from iron scrap in a process for regenerating iron scraps.
2. Description of the Related Art
To avoid a drop in the quality of iron produced by the regeneration of scrap, it is necessary to prevent the infiltration of non-ferrous impurity elements such as copper, zinc, tin and the like which are usually called tramp elements. Zinc and tin chiefly exist on the surface layers of plated steel plates, whereas copper exists, chiefly in the form of copper wire, in the motor cores of automobiles and household electric appliances. Therefore, the most effective method of preventing the infiltration of copper is to discriminate and separate copper in the stage of pulverization into scrap.
At the site for regenerating scraps, so far, scrap consisting chiefly of motor cores containing copper are discriminated, by eye, by the workers. However, the discrimination operation based upon the human eye involves problems; i.e., (1) it is difficult to increase the amount of scrap processed, (2) it is economically difficult to spend large amounts on labor cost, (3) it is difficult to maintain uniform quality of the scrap after the copper is removed, (4) it is difficult to improve the working environment, etc.
In order to automatically carry out this operation, there has been proposed a method of automatically discriminating the scrap by irradiation with a laser beam (Dr. H.-P Sattler: VDI BERICHTE NR. 934, 1991: Scrap Sorting with Laser--An Automatic Process for Mixed Non-Ferrous Metals from Automobile Shredders).
However, the above-mentioned method utilizes an expensive pulse laser irradiator which makes it difficult to cut the cost of the apparatus. Besides, the laser device and the spectroscope must be used in an adverse environment, requiring cost and labor for the maintenance of the apparatus. In order to automatically discriminate the scrap containing copper at a low cost, the present inventors have already filed a patent application covering an automatic discrimination method based upon the hue angle (Japanese Unexamined Patent Publication (Kokai) No. 6-323912; Method of Discriminating Scrap Containing Copper from Iron Scrap). According to the method based upon the hue angle only, however, the hue angle loses stability in scrap where the saturation value is low, and the precision of discriminating copper from iron decreases. Therefore, a first requirement for the present invention is to improve the discrimination precision in the method of automatically discriminating scrap containing copper relying upon the hue angle.
A motor core, which is the main source of mixing copper has copper wires and core which are mechanically entangled together and cannot be separated by magnetic separation. Therefore, copper and iron are discriminated, by eye, by the workers and are separated by hand as the motor cores are conveyed on a belt conveyer.
As an apparatus for sorting the wastes utilizing a difference in color, there has been proposed, for example, a cullet separator depending upon color as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 5-96249. According to this apparatus, the glass cullets are automatically sorted depending upon the color. That is, the colors of the cullets are discriminated by color images from a CCD camera, and a sorting drum having an air suction port is driven depending upon the color of a cullet that is to be sorted. However, this method is not utilizable for discriminating the scraps like those of the motor cores that include the colors of iron and copper in a mixed manner with other iron scrap.
In order to separate the copper-containing scrap after the discrimination and separation processing, it is necessary to recognize the individual scraps in the discrimination processing and to find position data for the copper-containing scrap.
Therefore, a second requirement of the present invention is to create a discrimination method which makes it possible to precisely discriminate the copper-containing scrap which has iron and copper color, like the scrap of motor cores, from iron scrap, and to obtain position data for the copper-containing scrap.
According to the above-mentioned discrimination method using a laser beam, the individual bits of scrap must be reliably irradiated with the laser beam making it necessary to arrange the individual scraps in alignment. Therefore, an aligning device must be employed. Besides, the processing efficiency becomes very low.
Therefore, a third requirement of the present invention is to realize a discriminating/separating apparatus for efficiently and automatically separating copper-containing scrap, like motor cores, from the scrap in which is mixed other iron scrap.
Furthermore, a method has been proposed for shock-pulverizing the iron scraps by cooling them to a temperature at which they become brittle as disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 48-24351.
According to this method, the whole scrap a part of which has magnetic properties is cooled and shock-pulverized though the ratio of the scrap groups having magnetic properties to the whole scrap is merely several percent by weight after pulverized at normal temperature. Therefore, this method is not economically efficient since a liquefied gas which is the method of cooling is very expensive, and this method is not utilized for separating scrap into copper scrap and iron scrap.
Therefore, a fourth requirement of present invention is to provide a method which automatically discriminates and separates scrap having magnetic properties from the scrap pulverized at normal temperature, i.e., automatically discriminates and separates scrap in which are mixed iron scrap and copper-containing scrap such as the scrap from motor cores, shock-pulverizes the scrap that is separated as copper-containing scrap by cooling them to a temperature lower than the temperature at which iron undergoes brittle fracture, and magnetically sorts the thus pulverized scrap to completely separate it into iron scrap and copper scrap, making it possible to regenerate large amounts of scrap at a low cost without relying upon human hands.